Colloid

Photo by: Ivaylo Ivanov

Colloids are mixtures whose particles are larger than the size of a
molecule but smaller than particles that can be seen with the naked eye.
Colloids are one of three major types of mixtures, the other two being
solutions and suspensions. The three kinds of mixtures are distinguished
by the size of the particles that make them up. The particles in a
solution are about the size
of molecules, approximately 1 nanometer (1 billionth of a meter) in
diameter. Those that make up suspensions are larger than 1,000 nanometers.
Finally, colloidal particles range in size between 1 and 1,000 nanometers.
Colloids are also called colloidal dispersions because the particles of
which they are made are dispersed, or spread out, through the mixture.

Types of colloids

Colloids are common in everyday life. Some examples include whipped cream,
mayonnaise, milk, butter, gelatin, jelly, muddy water, plaster, colored
glass, and paper.

Every colloid consists of two parts: colloidal particles and the
dispersing medium. The dispersing medium is the substance in which the
colloidal particles are distributed. In muddy water, for example, the
colloidal particles are tiny grains of sand, silt, and clay. The
dispersing medium is the water in which these particles are suspended.

Colloids can be made from almost any combination of gas, liquid, and
solid. The particles of which the colloid is made are called the dispersed
material. Any colloid consisting of a solid dispersed in a gas is called a
smoke. A liquid dispersed in a gas is referred to as a fog.

Types of Colloids

Dispersed Material

Dispersed in Gas

Dispersed in Liquid

Dispersed in Solid

Gas (bubbles)

Not possible

Foams:
soda pop; whipped cream; beaten egg whites

Solid foams:
plaster; pumice

Liquid (droplets)

Fogs:
mist; clouds; hair sprays

Emulsions:
milk; blood; mayonnaise

butter; cheese

Solid (grains)

Smokes:
dust; industrial smoke

Sols and gels:
gelatin; muddy water; starch solution

Solid sol:
pearl; colored glass; porcelain; paper

Properties of colloids

Each type of mixture has special properties by which it can be identified.
For example, a suspension always settles out after a certain period
of time. That is, the particles that make up the suspension separate from
the medium in which they are suspended and fall to the bottom of a
container. In contrast, colloidal particles typically do not settle out.
Like the particles in a solution, they remain in suspension within the
medium that contains them.

Colloids also exhibit Brownian movement. Brownian movement is the random
zigzag motion of particles that can be seen under a microscope. The motion
is caused by the collision of molecules with colloid particles in the
dispersing medium. In addition, colloids display the Tyndall effect. When
a strong light is shone through a colloidal dispersion, the light beam
becomes visible, like a column of light. A common example of this effect
can be seen when a spotlight is turned on during a foggy night. You can
see the spotlight beam because of the fuzzy trace it makes in the fog (a
colloid).

Light shining through a solution of sodium hydroxide (left) and a
colloidal mixture. The size of colloidal particles makes the mixture,
which is neither a solution nor a suspension, appear cloudy.
(Reproduced by permission of

Solution is mixture of 2 or more substances in equal proportion such as sugar or salt in water.But to differentiate colloid and suspension solution,there is big diff. that in colloidal solution,size of colloidal particle is in between 1 to 1000 nm and they show scattering of light(even though they r not visible with naked eye) and for suspension solution,suspended particles r in range of size of more than 1000 nm.These particles can be seen through naked eyes.